The invention relates to a magneto-optical memory element comprising a nonmagnetizable substrate having a layer of an amorphous material thereon. The amorphous material has a uniaxial magnetic anisotropy and it is an alloy of a rare-earth metal and a transition metal.
Such memory elements are known from U.S. Pat. No. 3,949,387 (same as German Auslegeschrift No. 23 40 475). The amorphous layer, in this patent, consists of a binary or a ternary composition the components of which belong to the 3d, 4f and 5f series elements of the periodic table.
Alloys of rare-earth metals and transition metals, when manufactured under certain conditions, are characterized by an amorphous structure, ferrimagnetic properties and, in the case of a layered construction, a uniaxial magnetic anisotropy which is perpendicular to the surfaces of the layer.
When a magneto-optical memory element having such an amorphous layer is locally heated to a temperature which is near either the compensation temperature or the Curie temperature of the material of the layer, for example by means of a focused laser beam, the heated area of the layer can be magnetized in a desired direction perpendicular to the surface of the layer by applying an external magnetic field extending perpendicular to the surface of the layer. After cooling the heated area of the layer, the coercive field strength must be sufficient to stabilize the magnetically varied area of the layer (the domain). The size of a stabilized area of the layer may be a few micrometers in diameter. An information value which corresponds to a logic "1" or "0" is assigned to such an area of the layer according to the direction of the magnetization in the interior of the area. Depending on the temperature up to which the layer is heated, the above-described process is referred to as compensation point switching or Curie point switching, respectively.
By means of a linearly polarized light beam, the magnetization direction of the area of the layer, and hence the information content thereof, can be determined as a result of the magneto-optical Faraday effect or Kerr effect. The magneto-optical rotation (Kerr rotation and Faraday rotation) of the known layers, however, is not too large. For example, the Faraday rotation of GdFe, at room temperature measured with light of a wavelength of 633 nm, is 1.7.times.10.sup.5 degrees per centimeter (.degree./cm.).